1. Field of the Invention
The present invention relates to single walled and multi-walled carbon nanotubes (CNTs), functionalized carbon nanotubes and carbon nanotube composites with controlled properties, to a method for aerosol synthesis of single walled and multi-walled carbon nanotubes, functionalized carbon nanotubes and carbon nanotube composites with controlled properties from pre-made catalyst particles and a carbon source in the presence of reagents and additives, to functional, matrix and composite materials composed thereof and structures and devices fabricated from the same in continuous or batch CNT reactors.
2. Description of Related Art
Carbon nanotubes are of great interest since they exhibit unique and useful chemical and physical properties related to, for instance, their morphology, toughness, electrical and thermal conductivity and magnetic properties. Since their discovery, CNTs have been the subject of intensive research and numerous patents, scientific articles and books have been devoted to their synthesis, properties and applications. Nanotubes were first observed during a direct-current arc discharge between graphite electrodes in an argon environment by lijima (Nature 1991, 354, 56). The typical temperatures for carbon nanotube production by that method are about 2000-3000° C. Since then, various authors described alternative means of carbon nanotubes production, which allowed increased production rate and significantly decreased temperatures, e.g., [Jiao and Seraphin, J. Phys. & Chem. Solids 2000, 61, 1055; Hafner et al., Chem. Phys. Lett. 1998, 296, 195]. For instance, it has been shown that the presence of transition metals decreases the typical temperature required for tube production (e.g., Jung et al., Diamond and Related Materials 2001, 10, 1235; Govindaraj et al., Materials Research Bulletin 1998, 33, 663; Shyu and Hong, Diamond and Related Materials 2001, 10, 1241). Since their discovery, several different production methods have been introduced to synthesize CNTs. These methods can be broadly divided into chemical and physical according to the method applied in releasing carbon atoms from carbon-containing precursor molecules. In the physical methods, e.g. arc-discharge (Iijima, Nature 1991, 354, 56) and laser ablation (Guo et al., Chem. Phys. Lett. 1995, 243 49), high-energy input is used to release the carbon atoms needed for tube synthesis. The chemical methods rely on carbon atomization via catalytic decomposition of carbon precursors on the surface of transition metal particles. According to the place where the growth of CNTs occur, chemical methods for their production can be divided into surface supported, so called CVD (chemical vapor deposition) [e.g. Dai et al., Chem. Phys. Lett. 1996, 260, 471] and aerosol [e.g. Bladh, Falk, and Rohmund, Appl. Phys. A, 2000, 70 317; Nasibulin et al., Carbon, 2003, 41, 2711] syntheses. In CVD methods, the carbon precursor decomposition and CNT formation take place on the surface of catalyst particles that are supported on a substrate. In aerosol synthesis, the catalyst particles are in the gas-phase. The terms “gas-phase synthesis” and “floating catalyst method” have been also applied in the literature for this process. We use the term “aerosol synthesis” to specify processes taking place completely in the gas-phase.
The method described in this patent is a new approach to the production of single walled and multi-walled CNTs, functionalized CNTs and CNT composite materials and matrices thereof. This new method requires pre-made catalyst particles or a procedure to produce pre-made catalyst particles with a narrow distribution of properties, a carbon source, a reagent, when needed, an energy source, when needed and a flow control system. A principle advantage of the new method over existing methods is that it allows the separate control of the introduction of catalyst particles and the CNT synthesis. In other methods, catalyst particles are formed by gaseous chemical reactions leading to the formation of supersaturated vapor of the catalyst material (e.g. WO 00/26138) or physical nucleation directly from supersaturated gas (e.g. WO 03/056078) simultaneously with the CNT synthesis and thus cannot be separately controlled. This leads to the formation of CNTs with potentially large variation in important properties such as length, diameter and chirality. The diameter and chirality of the CNTs produced via catalysts are largely determined by the properties of the catalyst particles, in particular the catalyst size. Though patent US 2002/102193 A describes a means of separately producing catalyst particles and CNTs, it does not specify a means of controlling the high non-uniformity of catalyst particles produced by the chemical nucleation method proposed and thus will tend to produce non-uniform CNTs. Our invention, on the other hand, provides a means of separately introducing catalyst particles with well controlled properties, either directly though a process which inherently produces catalysts with narrow particle size distributions (e.g. the physical vapor nucleation processes described in this method), or by providing specific means of narrowing the size distribution from processes (such as the chemical nucleation method referred to in US 2002/102193 A) which inherently produce wide catalyst particle size distributions and thus non-uniform CNTs. As the industrial and scientific utility of produced CNTs is a function of their individual and collective properties, there exists an urgent need for CNTs and a method for production of CNTs and CNT composite formulations with more uniform and controlled properties.
In our method we utilize pre-made particles for production of CNTs and CNT composite formulations. Those pre-made particles can be prepared by conventional methods such as chemical vapor decomposition of catalyst precursor [e.g. Nasibulin et al., J. Phys. Chem. B, 2001, 105, 11067.], by the physical vapor nucleation method, which implies an evaporation and subsequent vapor nucleation followed by growth of particles due to vapor condensation and cluster coagulation (for instance, a resistively heated hot wire generator, an adiabatic expansion in a nozzle or an arc discharge method), by thermal decomposition of precursor solution droplets (e.g. by electrospray thermal decomposition) or by any available method which either inherently produces particles with a narrow distribution of properties or can be pre-classified prior to CNT synthesis to narrow the distribution. The pre-made particles are then introduced into a CNT reactor where CNT synthesis takes place. Thus, the current invention separates the catalyst production from the CNT synthesis and allows the control of each step in the production process. In order to produce CNTs with further controlled properties, the pre-made particles, either produced as part of the process or introduced from existing sources, can be classified according to size, mobility, morphology or other properties before being introduced into one or more CNT reactors. Furthermore, the current invention allows the continuous or batch production of composite CNT either coated or mixed with additive materials. Additionally, the current invention provides a means of producing pure, functionalized or composite CNT gas, liquid or solid dispersions, solid structures, powders, pastes, colloidal suspensions and surface depositions and can be integrated directly into a means of fabricating structures from such materials. Additionally, when used in conjunction with the physical nucleation method, the current invention provides the additional advantage of allowing better control over conditions in the CNT reactor conditions since physical nucleation introduces no additional chemical compounds into the environment which can interfere with CNT formation, growth, purification and/or functionalization.